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Merge Merge/MergeBy/MergeJoinBy implementations (v2) #736

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merged 5 commits into from
Sep 20, 2023
Merged

Merge Merge/MergeBy/MergeJoinBy implementations (v2) #736

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23d8346
`MergeJoinBy` alias of new `InternalMergeJoinBy`
Philippe-Cholet Aug 24, 2023
1d0d801
Make `MergeBy` an alias of `InternalMergeJoinBy`
Philippe-Cholet Aug 24, 2023
535310b
Implement `FusedIterator` for `InternalMergeJoinBy`
Philippe-Cholet Aug 24, 2023
2ce8986
Unalias `MergeBy`
Philippe-Cholet Aug 31, 2023
9e267b6
Remove `OrderingOrBool::Out`
Philippe-Cholet Sep 20, 2023
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1 change: 0 additions & 1 deletion src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1075,7 +1075,6 @@ pub trait Itertools: Iterator {
where
J: IntoIterator,
F: FnMut(&Self::Item, &J::Item) -> T,
T: merge_join::OrderingOrBool<Self::Item, J::Item>,
Self: Sized,
{
merge_join_by(self, other, cmp_fn)
Expand Down
227 changes: 97 additions & 130 deletions src/merge_join.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
use std::cmp::Ordering;
use std::fmt;
use std::iter::Fuse;
use std::iter::{FusedIterator, Peekable};
use std::iter::{Fuse, FusedIterator};
use std::marker::PhantomData;

use either::Either;

Expand All @@ -11,19 +11,9 @@ use crate::size_hint::{self, SizeHint};
#[cfg(doc)]
use crate::Itertools;

pub trait MergePredicate<T> {
fn merge_pred(&mut self, a: &T, b: &T) -> bool;
}

#[derive(Clone, Debug)]
pub struct MergeLte;

impl<T: PartialOrd> MergePredicate<T> for MergeLte {
fn merge_pred(&mut self, a: &T, b: &T) -> bool {
a <= b
}
}

/// An iterator adaptor that merges the two base iterators in ascending order.
/// If both base iterators are sorted (ascending), the result is sorted.
///
Expand Down Expand Up @@ -62,103 +52,25 @@ where
///
/// See [`.merge_by()`](crate::Itertools::merge_by) for more information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MergeBy<I, J, F>
where
I: Iterator,
J: Iterator<Item = I::Item>,
{
a: Peekable<I>,
b: Peekable<J>,
fused: Option<bool>,
cmp: F,
}

impl<I, J, F> fmt::Debug for MergeBy<I, J, F>
where
I: Iterator + fmt::Debug,
J: Iterator<Item = I::Item> + fmt::Debug,
I::Item: fmt::Debug,
{
debug_fmt_fields!(MergeBy, a, b);
}

impl<T, F: FnMut(&T, &T) -> bool> MergePredicate<T> for F {
fn merge_pred(&mut self, a: &T, b: &T) -> bool {
self(a, b)
}
pub struct MergeBy<I: Iterator, J: Iterator, F> {
left: PutBack<Fuse<I>>,
right: PutBack<Fuse<J>>,
cmp_fn: F,
}

/// Create a `MergeBy` iterator.
pub fn merge_by_new<I, J, F>(a: I, b: J, cmp: F) -> MergeBy<I::IntoIter, J::IntoIter, F>
where
I: IntoIterator,
J: IntoIterator<Item = I::Item>,
F: MergePredicate<I::Item>,
{
MergeBy {
a: a.into_iter().peekable(),
b: b.into_iter().peekable(),
fused: None,
cmp,
left: put_back(a.into_iter().fuse()),
right: put_back(b.into_iter().fuse()),
cmp_fn: cmp,
}
}

impl<I, J, F> Clone for MergeBy<I, J, F>
where
I: Iterator,
J: Iterator<Item = I::Item>,
Peekable<I>: Clone,
Peekable<J>: Clone,
F: Clone,
{
clone_fields!(a, b, fused, cmp);
}

impl<I, J, F> Iterator for MergeBy<I, J, F>
where
I: Iterator,
J: Iterator<Item = I::Item>,
F: MergePredicate<I::Item>,
{
type Item = I::Item;

fn next(&mut self) -> Option<Self::Item> {
let less_than = match self.fused {
Some(lt) => lt,
None => match (self.a.peek(), self.b.peek()) {
(Some(a), Some(b)) => self.cmp.merge_pred(a, b),
(Some(_), None) => {
self.fused = Some(true);
true
}
(None, Some(_)) => {
self.fused = Some(false);
false
}
(None, None) => return None,
},
};
if less_than {
self.a.next()
} else {
self.b.next()
}
}

fn size_hint(&self) -> (usize, Option<usize>) {
// Not ExactSizeIterator because size may be larger than usize
size_hint::add(self.a.size_hint(), self.b.size_hint())
}
}

impl<I, J, F> FusedIterator for MergeBy<I, J, F>
where
I: FusedIterator,
J: FusedIterator<Item = I::Item>,
F: MergePredicate<I::Item>,
{
}

/// Return an iterator adaptor that merge-joins items from the two base iterators in ascending order.
///
/// [`IntoIterator`] enabled version of [`Itertools::merge_join_by`].
Expand All @@ -171,23 +83,29 @@ where
I: IntoIterator,
J: IntoIterator,
F: FnMut(&I::Item, &J::Item) -> T,
T: OrderingOrBool<I::Item, J::Item>,
{
MergeJoinBy {
MergeBy {
left: put_back(left.into_iter().fuse()),
right: put_back(right.into_iter().fuse()),
cmp_fn,
cmp_fn: MergeFuncLR(cmp_fn, PhantomData),
}
}

/// An iterator adaptor that merge-joins items from the two base iterators in ascending order.
///
/// See [`.merge_join_by()`](crate::Itertools::merge_join_by) for more information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MergeJoinBy<I: Iterator, J: Iterator, F> {
left: PutBack<Fuse<I>>,
right: PutBack<Fuse<J>>,
cmp_fn: F,
pub type MergeJoinBy<I, J, F> =
MergeBy<I, J, MergeFuncLR<F, <F as FuncLR<<I as Iterator>::Item, <J as Iterator>::Item>>::T>>;

#[derive(Clone, Debug)]
pub struct MergeFuncLR<F, T>(F, PhantomData<T>);

pub trait FuncLR<L, R> {
type T;
}

impl<L, R, T, F: FnMut(&L, &R) -> T> FuncLR<L, R> for F {
type T = T;
}

pub trait OrderingOrBool<L, R> {
Expand All @@ -197,20 +115,20 @@ pub trait OrderingOrBool<L, R> {
// "merge" never returns (Some(...), Some(...), ...) so Option<Either<I::Item, J::Item>>
// is appealing but it is always followed by two put_backs, so we think the compiler is
// smart enough to optimize it. Or we could move put_backs into "merge".
fn merge(self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult);
fn merge(&mut self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult);
fn size_hint(left: SizeHint, right: SizeHint) -> SizeHint;
}

impl<L, R> OrderingOrBool<L, R> for Ordering {
impl<L, R, F: FnMut(&L, &R) -> Ordering> OrderingOrBool<L, R> for MergeFuncLR<F, Ordering> {
type MergeResult = EitherOrBoth<L, R>;
fn left(left: L) -> Self::MergeResult {
EitherOrBoth::Left(left)
}
fn right(right: R) -> Self::MergeResult {
EitherOrBoth::Right(right)
}
fn merge(self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult) {
match self {
fn merge(&mut self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult) {
match self.0(&left, &right) {
Ordering::Equal => (None, None, EitherOrBoth::Both(left, right)),
Ordering::Less => (None, Some(right), EitherOrBoth::Left(left)),
Ordering::Greater => (Some(left), None, EitherOrBoth::Right(right)),
Expand All @@ -228,16 +146,16 @@ impl<L, R> OrderingOrBool<L, R> for Ordering {
}
}

impl<L, R> OrderingOrBool<L, R> for bool {
impl<L, R, F: FnMut(&L, &R) -> bool> OrderingOrBool<L, R> for MergeFuncLR<F, bool> {
type MergeResult = Either<L, R>;
fn left(left: L) -> Self::MergeResult {
Either::Left(left)
}
fn right(right: R) -> Self::MergeResult {
Either::Right(right)
}
fn merge(self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult) {
if self {
fn merge(&mut self, left: L, right: R) -> (Option<L>, Option<R>, Self::MergeResult) {
if self.0(&left, &right) {
(None, Some(right), Either::Left(left))
} else {
(Some(left), None, Either::Right(right))
Expand All @@ -249,7 +167,49 @@ impl<L, R> OrderingOrBool<L, R> for bool {
}
}

impl<I, J, F> Clone for MergeJoinBy<I, J, F>
impl<T, F: FnMut(&T, &T) -> bool> OrderingOrBool<T, T> for F {
type MergeResult = T;
fn left(left: T) -> Self::MergeResult {
left
}
fn right(right: T) -> Self::MergeResult {
right
}
fn merge(&mut self, left: T, right: T) -> (Option<T>, Option<T>, Self::MergeResult) {
if self(&left, &right) {
(None, Some(right), left)
} else {
(Some(left), None, right)
}
}
fn size_hint(left: SizeHint, right: SizeHint) -> SizeHint {
// Not ExactSizeIterator because size may be larger than usize
size_hint::add(left, right)
}
}

impl<T: PartialOrd> OrderingOrBool<T, T> for MergeLte {
type MergeResult = T;
fn left(left: T) -> Self::MergeResult {
left
}
fn right(right: T) -> Self::MergeResult {
right
}
fn merge(&mut self, left: T, right: T) -> (Option<T>, Option<T>, Self::MergeResult) {
if left <= right {
(None, Some(right), left)
} else {
(Some(left), None, right)
}
}
fn size_hint(left: SizeHint, right: SizeHint) -> SizeHint {
// Not ExactSizeIterator because size may be larger than usize
size_hint::add(left, right)
}
}

impl<I, J, F> Clone for MergeBy<I, J, F>
where
I: Iterator,
J: Iterator,
Expand All @@ -260,32 +220,31 @@ where
clone_fields!(left, right, cmp_fn);
}

impl<I, J, F> fmt::Debug for MergeJoinBy<I, J, F>
impl<I, J, F> fmt::Debug for MergeBy<I, J, F>
where
I: Iterator + fmt::Debug,
I::Item: fmt::Debug,
J: Iterator + fmt::Debug,
J::Item: fmt::Debug,
{
debug_fmt_fields!(MergeJoinBy, left, right);
debug_fmt_fields!(MergeBy, left, right);
}

impl<I, J, F, T> Iterator for MergeJoinBy<I, J, F>
impl<I, J, F> Iterator for MergeBy<I, J, F>
where
I: Iterator,
J: Iterator,
F: FnMut(&I::Item, &J::Item) -> T,
T: OrderingOrBool<I::Item, J::Item>,
F: OrderingOrBool<I::Item, J::Item>,
{
type Item = T::MergeResult;
type Item = F::MergeResult;

fn next(&mut self) -> Option<Self::Item> {
match (self.left.next(), self.right.next()) {
(None, None) => None,
(Some(left), None) => Some(T::left(left)),
(None, Some(right)) => Some(T::right(right)),
(Some(left), None) => Some(F::left(left)),
(None, Some(right)) => Some(F::right(right)),
(Some(left), Some(right)) => {
let (left, right, next) = (self.cmp_fn)(&left, &right).merge(left, right);
let (left, right, next) = self.cmp_fn.merge(left, right);
if let Some(left) = left {
self.left.put_back(left);
}
Expand All @@ -298,7 +257,7 @@ where
}

fn size_hint(&self) -> SizeHint {
T::size_hint(self.left.size_hint(), self.right.size_hint())
F::size_hint(self.left.size_hint(), self.right.size_hint())
}

fn count(mut self) -> usize {
Expand All @@ -310,7 +269,7 @@ where
(None, Some(_right)) => break count + 1 + self.right.into_parts().1.count(),
(Some(left), Some(right)) => {
count += 1;
let (left, right, _) = (self.cmp_fn)(&left, &right).merge(left, right);
let (left, right, _) = self.cmp_fn.merge(left, right);
if let Some(left) = left {
self.left.put_back(left);
}
Expand All @@ -328,13 +287,13 @@ where
match (self.left.next(), self.right.next()) {
(None, None) => break previous_element,
(Some(left), None) => {
break Some(T::left(self.left.into_parts().1.last().unwrap_or(left)))
break Some(F::left(self.left.into_parts().1.last().unwrap_or(left)))
}
(None, Some(right)) => {
break Some(T::right(self.right.into_parts().1.last().unwrap_or(right)))
break Some(F::right(self.right.into_parts().1.last().unwrap_or(right)))
}
(Some(left), Some(right)) => {
let (left, right, elem) = (self.cmp_fn)(&left, &right).merge(left, right);
let (left, right, elem) = self.cmp_fn.merge(left, right);
if let Some(left) = left {
self.left.put_back(left);
}
Expand All @@ -355,10 +314,10 @@ where
n -= 1;
match (self.left.next(), self.right.next()) {
(None, None) => break None,
(Some(_left), None) => break self.left.nth(n).map(T::left),
(None, Some(_right)) => break self.right.nth(n).map(T::right),
(Some(_left), None) => break self.left.nth(n).map(F::left),
(None, Some(_right)) => break self.right.nth(n).map(F::right),
(Some(left), Some(right)) => {
let (left, right, _) = (self.cmp_fn)(&left, &right).merge(left, right);
let (left, right, _) = self.cmp_fn.merge(left, right);
if let Some(left) = left {
self.left.put_back(left);
}
Expand All @@ -370,3 +329,11 @@ where
}
}
}

impl<I, J, F> FusedIterator for MergeBy<I, J, F>
where
I: Iterator,
J: Iterator,
F: OrderingOrBool<I::Item, J::Item>,
{
}